The invention relates to turbine engines, in particular aeroengines or industrial turbines, and it relates more particularly to guide vane assemblies having hollow airfoils for a turbine nozzle or a compressor diffuser.
Increasing the performance of turbine engines and reducing their polluting emissions leads to envisaging ever-higher operating temperatures.
For hot portion elements of turbine engines, proposals have therefore been made to use ceramic materials having a matrix that is constituted at least mostly by a ceramic (CMC). Such materials possess remarkable thermostructural properties, i.e. mechanical properties that make them suitable for constituting structural elements, with the ability to conserve these properties at high temperatures. Furthermore, CMC materials are of density that is much smaller than that of the metal materials conventionally used for hot portion elements of turbine engines.
Thus, Documents WO 2010/061140, WO 2010/116066, and WO 2011/080443 describe making rotor wheel blades for turbine engines out of CMC with inner and outer platforms incorporated in the blades. The use of CMC materials for turbine nozzles has also been proposed, in particular in Document WO 2010/146288.
It is also well known to make turbine nozzles, in particular low pressure nozzles, with vanes having hollow airfoils, i.e. airfoils that present internal longitudinal passages along their entire length between their outer and inner ends. Such passages enable a stream of ventilation air to be conveyed from the outside towards the inside, in particular for cooling the disks of rotor wheels of the turbine.
A nozzle sector made of composite material with hollow blades is described in Document US 2011/0008156. The fiber reinforcement of the composite material is made up of a stack of two-dimensional plies, some of the reinforcing plies of the airfoil extending to a thick upstream end portion of the outer platform of the sector.